Technical Field
The present disclosure relates to an image forming apparatus including a fixing device.
Description of the Related Art
An electrophotographic image forming apparatus includes a fixing device that melts a toner image and fixes the toner image on a sheet (transfer material). For example, a heat roller fixing device has a heating roller as a heating member and a pressure roller as a pressing member. By nipping and conveying the sheet at the pressure contact portion (nip portion) between the heating roller and the pressure roller, the unfixed toner image on the sheet is heated, and the toner image is fixed on the sheet.
Various methods for diagnosing deterioration of members constituting the fixing device have been conventionally proposed.
For example, JP 2016-130823 A discloses a method of diagnosing deterioration by detecting a temperature rise value of an elastic layer forming a nip portion.
JP 2007-212844 A and JP 2005-115221 A disclose a method of diagnosing deterioration by detecting the temperature of a fixing roller and measuring the time during which the temperature of the fixing roller is equal to or higher than a predetermined temperature.
In the recent trend of energy saving to reduce the environmental burden, low thermal conductivity of the members is often achieved. Along with this, even a member forming the nip portion is often provided with a material that reduces thermal conductivity. Reducing thermal conductivity makes it difficult for heat to be transferred to the interior, so that it is difficult for heat to become uniform, and a difference in temperature is liable to occur. That is, a temperature difference occurs between the temperature of the surface of the member forming the nip portion and the internal temperature.
Therefore, in a case where the surface temperature is detected, the actual internal temperature may be different from the surface temperature. In this case, for the fixing devices disclosed in JP 2016-130823 A, JP 2007-212844 A, and JP 2005-115221 A, it is difficult to precisely detect the internal temperature of the member forming the nip portion with a high degree of accuracy using the method of simply detecting the surface temperature, and it is difficult to execute deterioration diagnosis with a high degree of accuracy. It is also conceivable to provide a sensor, but there is concern about the complicated arrangement and increased cost of the sensor.